1. Field of the Invention
The present invention relates to hydraulic valve systems used, for example, in off-road earth moving, construction, and forestry equipment, such as backhoes, log loaders, feller bunchers, wheel loaders, and the like. Hydraulic valve systems are utilized, for example, to cause pistons to move a boom or bucket loader in a backhoe. The present invention relates to an improved design for such hydraulic valve systems.
2. Brief Description of the Related Art
Prior art hydraulic valve systems include the open center hydraulic valve system 110 illustrated in FIG. 1. The open center hydraulic valve system 110 in FIG. 1 is illustrated in a hydraulic circuit diagram in schematic form as would be understood by a skilled practitioner. The open center hydraulic valve system 110 of FIG. 1 presently is in common use, for example, in off-road earth moving, construction, and forestry equipment.
While variations in the basic design of such a prior art open center hydraulic valve system 110 exist, the fundamental components and operation of such a system are briefly described below.
The prior art open center hydraulic valve system 110 of FIG. 1 typically includes a hydraulic fluid tank 112, one or more constant flow open center hydraulic valve banks (“valves”) 114, and a fixed displacement pump 116. Each valve 114, in turn, may include one or more spools 118, with each spool 118 being activated by a spool actuator 120. The spool actuators 120 may be activated by an equipment operator using a number of known means (not illustrated), such as mechanically (for example, using a lever), electrically (for example, using a solenoid receiving an electrical signal from a switch, a joystick, a computer, or other means), hydraulically, pneumatically, or otherwise.
In order to illustrate the operation of a spool 118 to selectively interconnect hydraulic pathways within a valve, a simplified set of drawings illustrating how a spool 118 of a simple prior art constant flow open center (“CFO”) valve 136 is capable of redirecting the constant flow of hydraulic fluid is provided in FIGS. 2A, 2B, and 2C. There, spool 118 is capable of providing selective hydraulic communication with either of a pair of hydraulic ports 122 and 124, depending upon the position of spool 118. The hydraulic ports 122 and 124 are hydraulically connected to a cylinder 126 on either side of a piston 128. The simple CFO valve 136 has a number of internal hydraulic pathways which permit the spool 118, depending on its position, to direct hydraulic fluid flow to or from hydraulic ports 122 and 124.
For example, in FIG. 2A, the spool 118 is in the neutral position. In that position, fixed displacement pump 116 pumps hydraulic fluid at a constant rate through open center core 130. The spool 118 does not obstruct or restrict the hydraulic fluid flow through the open center core 130, which proceeds to the tank galley 132, and then through tank galley 132 to hydraulic fluid tank 112. The spool 118 in the neutral position blocks the flow of hydraulic fluid to or from hydraulic ports 122 and 124, on the one hand, and either the open center core 130 or the tank galley 132, on the other hand. The result is that no net hydraulic fluid flows into or out of cylinder 126 either above or below piston 128. The piston 128 and associated load 134 do not raise or lower.
In FIG. 2B, on the other hand, spool 118 is caused to move to a first non-neutral position (upward) where spool 118 partially restricts the hydraulic fluid flow provided by fixed displacement pump 116 through open center core 130, raising the hydraulic pressure of the hydraulic fluid upstream of the spool 118 (i.e., between the spool 118 and the fixed displacement pump 116). The spool 118 also opens a hydraulic pathway within the simple CFO valve 136 for net hydraulic fluid to flow from the open center core 130 through hydraulic port 122 into the cylinder 126 below the piston 128. At the same time, spool 118 opens a hydraulic pathway in simple CFO valve 136 between hydraulic port 124 and the tank galley 132 allowing net hydraulic fluid to flow out of the cylinder 126 above the piston 128 to the tank galley 132 and to hydraulic fluid tank 132. The result is that there is net hydraulic fluid flow into the cylinder 126 below the piston 128 and out of the cylinder 126 above the piston 128; thus, the piston 128 and its associated load 134 is caused to rise.
Further, in FIG. 2C, spool 118 is caused to move to a second non-neutral position (downward), causing spool 118 to partially restrict the hydraulic fluid flow provided by fixed displacement pump 116 through open center core 130, raising the hydraulic pressure upstream of the spool 118. The spool 118 opens a hydraulic pathway within the simple CFO valve 136 permitting net hydraulic fluid flow from the open center core 130 through hydraulic port 124 into the cylinder 126 above the piston 128, while at the same time opening a hydraulic pathway between hydraulic port 122 and tank galley 132 allowing net hydraulic fluid to flow out of the cylinder 126 below the piston 128. The result is that the piston 128 and its associated load 134 is lowered.
The operation of the spool 118 in the prior art open center hydraulic valve system 110 is similar to the operation of the spool 118 in the prior art simple CFO valve 136 described above; however, as illustrated and disclosed in the schematic diagram of FIG. 1, the fluid pathways within prior art open center hydraulic valve system 110 that are selectively interconnected by spool 118 differ to a certain extent.
Referring once again to the prior art open center hydraulic valve system 110 illustrated in FIG. 1, each spool 118 is capable of selective hydraulic communication with a pair of associated hydraulic ports 122 and 124. Each pair of hydraulic ports 122 and 124, in turn, may communicate hydraulically with equipment applications (such as a boom on a backhoe) in which the open center hydraulic valve system 110 is used to operate, typically utilizing a cylinder and a piston. The hydraulic ports selectively provide pressurized hydraulic flow to or from the cylinder on either side of the piston.
Referring again to FIG. 1, each spool 118 of each valve 114, and, hence, each pair of hydraulic ports 122 and 124 associated with each spool 118, is associated with a function of the application on the equipment within which the open center hydraulic valve system 110 is utilized. In the example illustrated in FIG. 1, one of the spools 118 (and the associated pair of ports 122 and 124) is associated with the each of the following functions, which can be found, for example, in a backhoe: boom, bucket, stick, swing, stabilizer, boom loader, bucket loader, and auxiliary. Those functions are chosen for purposes of illustration, and, as would be recognized by skilled practitioners, those functions can vary, depending on the equipment and applications to which the open center hydraulic valve system 110 is assigned.
The valves 114 include several hydraulic fluid pathways that may be selectively interconnected by activation of the spool 118, including an open center core 130, a power core 138, and a tank galley 132. The fixed displacement pump 116 pumps hydraulic fluid (at a constant flow rate for a given engine speed) from the hydraulic fluid tank 112 into the open center core 130. The tank galley 132 returns hydraulic fluid to the hydraulic fluid tank 112, where it is available to be re-pumped. The valves 114 also include a hydraulic connection between the open center core 130 and the power core 138, namely, an open center/power core passage 140. Typically, the valves 114 may also include smaller internal valves utilized to prevent, for example, overpressure or incorrect flow direction in the system, such as relief valves 142, or load drop check valves 144, which are not material to the explanation of the prior art or the invention.
The prior art open center hydraulic valve system 110 is typically housed in a standard manifold (not illustrated) attached to the equipment (e.g., construction, earth moving, or forestry equipment, such as a backhoe) in which the open center hydraulic valve system 110 is being used. The fixed displacement pump 116 is typically driven by a power take-off (not illustrated), which, in turn, is directly mounted to a transmission (not illustrated), which is connected to the prime mover of the equipment in which the prior art open center hydraulic valve system 110 is being used.
The operation of the spools 118 in each of the valves 114 to direct hydraulic fluid flow to and to permit fluid flow from associated hydraulic ports 122 and 124 to cause, for example, a piston to move within a cylinder and thereby cause movement of a functional aspect of the equipment on which the open center hydraulic valve 110 is mounted is well-known to skilled practitioners, and can be ascertained by skilled practitioners by reference solely to the schematic diagram found in FIG. 1. For purposes of the following explanation, hydraulic ports 122 and 124 will be assumed to be hydraulically connected to a cylinder 126 above and below a piston 128, respectively, in a manner similar to that illustrated in FIGS. 2A, 2B, and 2C.
As can be seen in FIG. 1, and will be described further below, when a spool 118 is caused by spool actuator 120 to be in the neutral position (with the open center core 130 unrestricted by the spool 118, and the fluid passageways between either the open center core 130 or the tank galley 132, on the one hand, and the pair of hydraulic ports 122 and 124 associated with the spool 118, on the other hand, being obstructed by the spool 118, no net hydraulic fluid flows to or from the hydraulic ports 122 and 124 to the cylinder 126 on either side of the piston 128, and thus, the piston 128 does not move. Instead, the hydraulic fluid delivered at a constant flow rate (for a given engine speed) by the fixed displacement pump 116 flows unrestricted through the open center core 130 and through the open center of the spools 118 to the tank galley 132 and to the hydraulic fluid tank 112 where it is re-pumped. Hence, the function to which the piston 128 and cylinder 126 is associated (e.g., the position of the boom) does not change, because there is no net change in hydraulic fluid in the cylinder 126 either above or below the piston 128. The piston 128 therefore does not move.
If, as shown in FIG. 1, the spool actuator 120 is activated by an operator to cause the spool 118 to move from the neutral position to a first non-neutral position, the constant flow of hydraulic fluid delivered by the fixed displacement pump 116 is caused by the partial restriction by the spool 118 of the open center core 130 to increase in pressure. Referring to FIG. 1, the increase in fluid pressure in the open center core 130 is communicated to the power core 138 through the open center/power core passage 140. As shown in FIG. 1, the activated spool 118 allows pressurized hydraulic fluid to flow from the power core 138 to the first hydraulic port 122 associated with the activated spool 118 into the cylinder 126 under the piston 128. The activated spool 118 simultaneously allows fluid to flow out of the cylinder 126 through the second hydraulic port 124 associated with the activated spool 118 which is connected above the piston 128. That fluid flows through the tank galley 132 to the hydraulic fluid tank 112 (where it is re-pumped). Thus, the net effect is that hydraulic fluid under pressure flows into the cylinder 126 below the piston 128, and hydraulic fluid flows out of the cylinder 126 above the piston 128. This causes the piston 128 and associated load 134 to rise and the function to change (e.g., it causes the boom and any associated load to rise).
On the other hand, if, as shown in FIG. 1, the spool operator manipulates the actuator 120 to cause the spool 118 to move from the neutral position to a second non-neutral position, that once again causes partial restriction of the open center 130, and causes the fluid flowing through the open center core 130 to increase in pressure. That increase in hydraulic pressure is once again communicated from the open center core 130 to the power core 138 through open center/power core passage 140. At the same time, hydraulic fluid is allowed by the activated spool 118 to flow out of the cylinder 126 under the piston 128 through the connected hydraulic port 122 associated with activated spool 118 and through the tank galley 132 to the hydraulic fluid tank 112. Also at the same time, the spool directs pressurized fluid (under pressure from the fixed displacement pump 116 due to partial restriction of the opening in the open center core 130 by the spool 118) to flow from the power core 138 through the associated hydraulic port 124 into the cylinder 126 above the piston 128. Thus, hydraulic fluid under pressure is introduced to the cylinder 126 above the piston 128, and hydraulic fluid is drained from the cylinder 126 below the piston 128. This causes the piston 128 to lower and the equipment function to change (e.g., the boom and any associated load is caused to lower). A skilled artisan would recognize, of course, that this activation of spools 118 in the valves 114 can be utilized to operate a number of different equipment functions having moving components, and would not be limited to booms (or to backhoes).
Further details of the operation of the prior art open center hydraulic valve system 110 illustrated in FIG. 1 are described below. The explanation herein concerning the operation of a single spool 118 (and its associated pair of hydraulic ports 122 and 124) within a single valve 114 associated with a particular single function is illustrative, and is not limited to that particular single spool 118 or valve 114, and applies to other spools 118 and valves 114 within the open center hydraulic valve system 110 as well.
Because the pump for the prior art open center hydraulic system 110 is a fixed displacement pump 116, the flow of the hydraulic fluid supplied by the fixed displacement pump 116 is constant for a given engine speed for the equipment in which the prior art open center hydraulic system 110 is mounted.
When the spool actuators 120 in the valves 114 in the prior art open center hydraulic system 110 are in the neutral position, all of the associated spools 118 are likewise in the neutral position. As illustrated in FIG. 1, the centers of the valve spools 118 are open, the net flow paths to the associated hydraulic ports 122 and 124 (from the open center core 130 or the power core 138), or from the hydraulic ports 122 and 124 (to the tank galley 132), are blocked by the spools 118, and all net hydraulic fluid flow pumped by the fixed displacement pump 116 from the hydraulic fluid tank 112 at a constant flow rate flows unrestricted through the open center core 130 through the spools 118 to the tank galley 132 and then back to the hydraulic fluid tank 112 where it is again available to be pumped.
When one of the functions associated with the prior art open center hydraulic system 110 is desired to be activated, the spool actuator 120 associated with that function is activated by an equipment operator in order to move the associated spool 118 (left or right, as shown in the schematic in FIG. 1) in order to partially restrict or “pinch” the opening through the open center core 130 to the tank galley 132. This partial restriction of hydraulic fluid flow by the spool 118 in the open center core 130 partially restricts flow to the tank galley 132, and, in turn, increases the pressure of the hydraulic fluid in the open center core 130 being provided at constant flow by the fixed displacement pump 116. The resulting increased hydraulic fluid pressure in the open center core 130 is transmitted hydraulically through the open center/power core passage 140 to the power core 138.
If the chosen spool actuator 120 is activated with the intention of causing the piston 128 to move to a first non-neutral position as illustrated in FIG. 1 (and to thereby, for example, lift a boom and associated load), then not only is the open center core 130 partially restricted to cause an increase in pressure to occur in the open center core 130 and be transmitted to the power core 138, but the spool 118 at the same time opens a hydraulic passage in the valve 114 between associated hydraulic port 122 (hydraulically connected to a cylinder 126 below the piston 128, in the manner illustrated in FIG. 2B) and the power core 138. The hydraulic fluid, having increased hydraulic pressure in the power core 138, is transmitted through associated hydraulic port 122. Simultaneously, activated spool 118 opens a hydraulic passage in the valve 114 between associated hydraulic port 124 (hydraulically connected to a cylinder 126 above the piston 128, in the manner illustrated in FIG. 2B) and the tank galley 132. The result is that hydraulic fluid under pressure from the power core 138 flows through associated hydraulic port 122 and begins filling the cylinder 126 below the piston 128, and hydraulic fluid is permitted to leave the cylinder 126 above the piston 128 by flowing through associated hydraulic port 124 into the tank galley 132 to return to the hydraulic fluid tank 112, where it is available to be re-pumped. By adding pressurized hydraulic fluid to the cylinder 126 below the piston 128, and by reducing hydraulic fluid in the cylinder 126 above the piston 128, the piston 128 and its associated load 134 is lifted.
Conversely, if the chosen spool actuator 120 is activated with the intention of causing the piston to move to a second non-neutral position as illustrated in FIG. 1, (and to, for example, cause a boom to lower), then not only does the activated spool 118 cause the open center core 130 to be partially restricted to cause an increase in fluid pressure in the open center core 130 to be hydraulically transmitted to the power core 138 via open center/power core passage 140, but also the activated spool 118 opens a hydraulic passage in the valve 114 between the associated hydraulic port 124 (hydraulically connected to cylinder 126 above the piston 128) and the power core 138 (with pressurized hydraulic fluid). Simultaneously, the activated spool 118 opens a passage in valve 114 between associated hydraulic port 122 (hydraulically connected to cylinder 126 below the piston 128, in the manner illustrated in FIG. 2C) and the tank galley 132, allowing hydraulic fluid to flow out of the cylinder 126 below the piston 128 to the tank galley 132 and the hydraulic fluid tank 112. The result is that hydraulic fluid under pressure from the power core 138 begins filling the cylinder 126 above the piston 128, and hydraulic fluid begins leaving the cylinder 126 below the piston 128. The piston 128 and its associated load 134 lowers (in this example, the boom and load is lowered).
Because the prior art open center hydraulic valve system 110 illustrated in FIG. 1 utilizes a fixed displacement pump 116 operating at a constant flow for a given engine speed for the equipment on which it is mounted, all power used to generate unused hydraulic fluid flow (such as hydraulic fluid constantly flowing through the open center core 130 when the spools 118 are in the neutral position) is a loss. Nevertheless, the size and power of the fixed displacement pump 116 in such a prior art system must accommodate not only sufficient hydraulic flow and system pressure to operate the multiple functions operated by the valves 114 at rated load conditions, but also must sustain the constant hydraulic flow through the open center core 130 (as well as overcome line losses) in order for the system to operate properly. A relatively large and powerful fixed displacement pump 116 running constantly is therefore required for the prior art open center hydraulic valve system 110. And, as noted above, a considerable portion of the power of the fixed displacement pump 116 in such a system is required to deliver hydraulic fluid flow that is frequently unused by the functions of the system, for example, the unused flow that constantly passes through the open center core 130 to the hydraulic fluid tank 112, only to be re-pumped (when one or more, often all, spools 118 are not activated and the functions are idle). Hence, significant inefficiencies are inherent in the prior art open center hydraulic valve system 110.
A number of factors have spurred equipment manufacturers and hydraulic systems designers to attempt to overcome the inefficiencies and shortcomings of the prior art prior art hydraulic valve systems, including open center hydraulic valve system 110. New emissions standards and a desire for fuel savings have caused designers and manufacturers to attempt to design equipment and hydraulic systems that are more fuel efficient, and more power efficient, by achieving greater horsepower management. Manufacturers and designers likewise desire to avoid significant increases in the size, weight, and expense of providing alternatives to the prior art systems, such as open center hydraulic valve systems 110.
For example, one potential alternative previously considered by designers and manufacturers was to replace the fixed displacement pump 116 of the open center hydraulic valve system 110 illustrated in FIG. 1 with a variable displacement piston pump (not illustrated). In such a potential alternative, however, the existing valves 114 in the prior art open center hydraulic valve system 110 would be required to be replaced by considerably larger, considerably heavier, and considerably more expensive valves in order to permit the higher hydraulic fluid flow required by such a replacement. Such a potential alternative therefore not only was largely rejected as being cost prohibitive, but the installation of such a large, heavy system was determined to be highly undesirable because, in many if not most applications, there is limited room available on equipment for the hydraulic system to be mounted.
The present invention, known as a fixed/variable hybrid system, overcomes the problems associated with both the prior art open center hydraulic valve system 110 and the potential alternatives that have been considered and largely rejected (for example, replacement of the fixed displacement pump 116 with a variable displacement piston pump). The fixed/variable hybrid system of the present invention achieves reduced emissions, greater horsepower management, and greater fuel savings, without greatly increasing the cost, size, or weight of the hydraulic valve system.